Research on hyperactivity (attention deficit disorder) suggests that problems identified at school-age have a relatively poor prognosis and tend to be resistant to treatment, particularly in youngsters who are also aggressive and/or from disturbed families. These findings highlight the importance of early identification of hyperactivity in young children and the development of appropriately targeted interventions. Although there is general agreement that hyperactivity has its onset in early childhood, prospective, developmental data on the correlates, course, and outcome of this disorder in young children are just beginning to appear. Lack of hard data reflects the formidable definitional and differential diagnostic problems inherent in the study of behavior disorders in young preschoolers, as well as the widespread belief that problems in early childhood are transient. Recent evidence, however, suggests that problems identified in very young children may persist. Further, family stress and early peer problems appear to be associated with continuing difficulties in social adjustment and academic achievement in early elementary school. Therefore, the research proposed in this application is geared to exploring the early development of hyperactive children. Our original sample of parent-referred 2 and 3 year olds will be followed up at age 9 to determine the nature and severity of problem behavior in elementary school. A new sample of preschoolers who meet DSM-III criteria for attention deficit disorder will also be studied using a convergent longitudinal design and a multifaceted assessment strategy. Focus will be on four issues: 1. the persistence of symptoms over time; 2. the contribution of family stress and dysfunction to follow-up status; 3. the relative contributions of symptoms of hyperactivity and aggression at intake to follow-up status; 4. the nature of peer interactions in hyperactive preschoolers and the relationship of early peer problems to follow-up status.